This invention relates to a gas-hydraulic pressure actuator for opening and closing a pipe line valve.
Gas-hydraulic pressure type actuators are commonly used for opening and closing ball valves in gas pipe lines. With such actuators, the gas being transported through the pipe line is used as the power source, and the gas pressure, rather than acting directly on the actuator cylinder, is applied to the upper portion of an oil filled pressure vessel. This converts the gas pressure to a hydraulic pressure, which is then tapped off from the lower portion of the pressure vessel and drivingly applied to the actuator cylinder. Such conversion of gas pressure into hydraulic pressure is advantageous because: the actuator cylinder is lubricated by the working oil; it is easier to control the opening and closing speed of the valve with oil as compared with gas; and if the gas pressure drops too low to power the actuator the valve can be opened or closed by operating a hydraulic hand pump.
A prior art actuator of this type is shown by way of example in FIG. 1, wherein reference numeral 1 designates a pipe line, 2 is a valve body, and 3 is a valve stem. A lever 4a of an actuator 4 is keyed to the valve stem 3, so as to open and close the valve in association with the stroke of the actuator piston. Gas outlet ports 2a and 2b in the upstream and downstream sides of the valve body are connected by pipes 5 and 6 to check valves 7 and 8, respectively. Outlet pipes 9 and 10 from the check valves merge into a pipe 11, which leads to a port 12p of an electromagnetic valve 12. A port 12a of the valve is connected to a gas inlet port 15a in the upper portion of a pressure vessel 15 by a pipe 13, while a port 12b of the valve 12 is connected to a gas inlet port 16a in the upper portion of a pressure vessel 16 by a pipe 14. The pressure vessels 15 and 16 are filled with a quantity of working oil such that when the valve 2 assumes an opening of 45.degree., the liquid level is maintained in the vertical mid portions of the vessels. Connected to oil outlet ports 15b and 16b in the lower portions of the pressure vessels are flow control valves 17 and 18, respectively, whose outlets are connected by pipes 19 and 20 to ports 21a and 21b of a change-over valve 21, respectively. The change-over valve has ports 21c and 21d connected to ports 4c and 4d of the actuator cylinder, and ports 21t and 21p connected to suction and discharge ports 22t and 22p of a hand pump 22, respectively.
In operation, some of the gas flowing through the pipe line 1 is released through whichever of the ports 2a or 2b is on the high pressure side, and arrives at the port 12p of the electromagnetic valve 12, irrespective of whether the valve 2 is open or closed. If the valve 12 is deenergized, the port 12p is blocked, while the ports 12a and 12b are open to the atmosphere, as shown in FIG. 1. If the solenoid 12Sa of the valve 12 is energized, the valve spool is shifted to the right as viewed in FIG. 1, thereby communicating the ports 12a and 12p with each other. This introduces gas through the pipe 13 to the pressure vessel 15, which forcibly discharges oil from the vessel. This oil passes through the flow control valve 17, pipe 19, valve 21, and the port 4d into the actuator cylinder 4, whereby the piston and piston rod 4b are urged to the left to open the valve 2. Simultaneously with such piston movement, the oil in the other side of the cylinder is discharged through the port 4c, valve 21, pipe 20 and flow control valve 18 into the pressure vessel 16. The flow rate of this oil is adjusted by the control valve 18, so that the speed of the actuator 4 in opening the valve 2 is thereby regulated. The upper portion of the pressure vessel 16 is vented to the atmosphere through the valve 12. After the valve 2 has been fully opened, the solenoid 12Sa is deenergized. Consequently, the valve spool resumes the position shown in FIG. 1, and the pressurized gas in vessel 15 is released through port 15a and valve 12 to the atmosphere. In a similar manner, if the solenoid 12Sb of the valve 12 is energized, the valve spool is shifted to the left and the actuator 4 will operate to close the valve 2.
If the gas pressure in the pipe line 1 becomes too low to produce sufficient hydraulic pressure to open the valve 2, then the valve 21 is shifted to the left. Consequently, the suction port 22t of the hand pump 22 becomes connected by way of ports 21t and 21a to the valve 17 below the pressure vessel 15. On the other hand, the discharge port 22p of the hand pump 22 is connected by way of ports 21p and 21d to the port 4d of the actuator cylinder. If, under these conditions, the hand pump 22 is operated, the valve 2 will be manually opened. In a similar manner, if the valve 21 is shifted to the right, the manual operation of the hand pump 22 will close the valve 2.
Such a prior art gas-hydraulic pressure type valve actuator imposes a number of system requirements. First, the pressure vessels 15 and 16 for converting the gas pressure into hydraulic pressure must be high pressure containers, and they must have a volume several times as large as the volume of oil displaced by one stroke of the actuator 4. Second, an increase in the size of the valve 2 greatly increases the cost of the actuator system. Third, since the pressure vessels 15 and 16 are normally vented to the atmosphere, a relatively large volume of gas is necessary to raise the pressure in the vessels to an operational level at the time of valve actuation, and such gas is subsequently lost when it is vented to the atmosphere. Stated otherwise, the volume of gas consumed or wasted during a valve actuation is several times the volume of the actuator cylinder.
Actually, it is highly advantageous for the actuator to convert a gas pressure into a hydraulic pressure. The use of pressure vessels for effecting such a conversion, however, is accompanied by a number of drawbacks, as described above.